The invention relates generally to accelerometers and, in particular, to capacitance-type accelerometers.
In the study of physical systems, it is often desirable to observe the motion of a system and, in particular, its acceleration. Accelerometers can be described as a combination of two transducers—a primary transducer, which converts acceleration of a mass into displacement, and a secondary transducer, which converts the displacement of the mass into an electric signal.
Capacitance accelerometers employ a capacitor between the mass and a support structure, and measure the variable capacitance between the two. More specifically, an acceleration of the mass causes a change in the space between moving and fixed plates of the capacitor. The change in the space or displacement of the moving plate relative to the fixed plate is inversely proportional to the charge on the capacitor.
Accelerometers are now being manufactured in Micro-Electro-Mechanical Systems (MEMS), which integrate mechanical elements, sensors and electronics on a common silicon substrate through the utilization of microfabrication technology. While the electronics are fabricated using integrated circuit processing sequences, the micro-mechanical components are fabricated using compatible “micro-machining” processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices. As the availability of accelerometer MEMS drives the use of accelerometers in small size, lightweight and lower cost sensing systems in all application domains, however, there is an ever increasing need for higher sensitivity and precision accelerometers.